1. Field of the Invention
The present invention relates to a communication technique in a communication system implementing a plurality of communication apparatuses for realizing between the communication apparatuses transmission/reception of an operation request and transmission/reception of an operation response to an operation request received from the communication counterpart.
2. Description of the Related Art
It is known that in a communication system connecting a plurality of communication apparatuses via a network, the communication apparatuses exchange messages with each other so that a communication apparatus is able to send a notification to a counterpart communication apparatus or command the counterpart apparatus to execute a request, for example. In such a system, a communication apparatus may send a command to execute an operation to another communication apparatus as an operation request and the communication apparatus receiving the operation request may send an execution result of the operation as an operation response.
Also, a technique is known in which a portion of the communication apparatuses making up the communication system are arranged to be communication clients and another portion of the communication apparatuses are arranged to be communication servers, and communication between a communication client and a communication server is realized by a protocol in which the communication client sends a communication request to the communication server and the communication server sends back a communication response to the communication client corresponding to a sender of the communication request.
In such a system, the communication client may describe an operation request in the communication request and send this to the communication server, and the communication server may describe the operation response to this operation request in the communication response and send this back to the communication client corresponding to the sender of the communication request.
Further, a reversal of the above technique is known in which the communication server sends an operation request to the communication client to administer the execution of an operation. In the following, exemplary implementations of such technology are described.
In Japanese Patent Laid Open Publication No.2001-273211, a message transmission/reception technique between a remote processor and a local processor is disclosed in which the remote processor sends a message indicating a command that is to be executed by the local processor and receives a response to the command from the local processor.
Also, according to this document, in a case where the local processor is stationed within a firewall, the local processor sends a communication request to the remote processor stationed outside the firewall so that a command can be sent to the local processor within the firewall from outside.
In this example, the local processor corresponds to the communication client and the remote processor corresponds to the communication server.
Also, the technology relating to the operation request can be used in a system for controlling the operation of an apparatus connected to the communication apparatus at a remote location. An example of such implementation is disclosed in Japanese Patent Laid Open Publication No.2002-135858. According to this document, in a remote operation system for operating blinds and lights, a remote operation apparatus having the function of accepting operations made by a user sends a command to a remotely controlled apparatus having the function of operating the blinds and lights. However, in this document, no mention is made of sending a response to the command.
In a case where messages are exchanged between a plurality of communication apparatuses, one of the communication apparatuses may correspond to the sender of commands. Alternatively, a plurality of communication apparatuses may be arranged to send commands to each other, in which case the communication apparatus receiving a command is arranged to send back an execution result to the sender of the command. In such an arrangement, information sent from one communication apparatus to a counterpart communication apparatus may be a command to the counterpart communication apparatus or an execution result of a command received from the counterpart communication apparatus.
In the conventional art, these commands and execution results are sent separately. In such a method, separate connections are respectively established for the time a command is to be sent and for the time an execution result of the received command is to be sent. In turn, the communication overhead is increased and thereby a problem in communication efficiency arises.
Presently, there are still many environments implementing the dial-up connection for establishing connection within a network. The above-described problem is particularly troublesome in such environments. Namely, in such environments, it may take several tens of seconds to establish a connection, and a fee is charged each time a connection is established. Therefore, an increase in the number of connections established results in a significant rise in costs.